Double-tuned ³¹P/¹H human head array with high performance at both frequencies for spectroscopic imaging at 9.4T

Purpose: To develop a robust design of a human head double-tuned ³¹P/¹H array, which provides good performance at both ³¹P and ¹H frequencies for MR spectroscopic imaging at 9.4T. Methods: Increasing the number of surface loops in a human head array improves the peripheral signal-to-noise ratio (SNR), while the central SNR doesn’t substantially change. High peripheral SNR can contaminate MR spectroscopic imaging data at both ¹H and ³¹P frequency. To minimize this effect, we limited the number of elements in the ³¹P array to 10, i.e., 8 transceiver surface loops circumscribing the head and 2 receive “vertical” loops placed at the superior location. The ¹H-portion of the array also consists of 10 elements, i.e., 8 transceiver surface loops circumscribing the head and 2 transceiver “vertical” loops at the superior location of the head. Both the ³¹P array and ¹H array are placed in a single layer at the same distance to the head, which provides high loading and, thus, a good performance for both arrays. Results: Transmit efficiency of the ¹H-portion of the double-tuned array was very similar to that of the single-tuned arrays of similar size. Also, addition of the cross-loops substantially improved the brain coverage. Conclusion: We developed a novel ³¹P/¹H double-tuned array for MR spectroscopic imaging of a human brain at 9.4T. Placing both ³¹P and ¹H loops in a single layer provides for high transmit efficiency at both frequencies without compromising SNR near the brain center at the ³¹P-frequency. Addition of the cross-loops at the superior location improves the brain coverage.